Your idea is a modifed variant on the original Hirsch-Meeks patent so often discussed on this list.

They use a dispenser cathode (electron source) and a close concentric shell grid to create the ions needed near the outer shell or wall only. The system can easily work into the high vacuum region of 10e-6 torr. (By letting the electrons serpentine about the grid region near the wall creating ions there only)

RF could work if loaded into the system properly. Try it and let us know how it works. Basically you are suggesting trading the dispenser cathode for an potent RF source.